The TDM/TDMA principle is well known in radio systems or passive optical networks (PONs), where it is employed to permit transmission between a single basestation and a plurality of outstations. In the downstream (basestation to outstation) direction, the information (traffic) is broadcast to all outstations, but upstream it is transmitted in bursts, each of which must be timed to avoid mutual interference (overlap) so that at any time the basestation only receives data from one outstation. When a new outstation is to be connected its time of transmission must be such that it does not interfere with existing traffic transmissions and the processing required to ensure this is referred to as marshalling.
In our co-pending U.S. application Ser. No. 08/152,278 the contents of which are hereby incorporated by reference, there is disclosed a method for measuring and aligning in time the transmissions of a new outstation which eliminates the possibility of it disrupting existing traffic, by employing sequences (pseudo random sequences) at a level below the noise sensitivity of the basestation receiver (for normal traffic). The sequences can be detected using correlation and their phase is used to determine the loop delay to the new outstation.
The present invention is based on the frame alignment process described in the above-mentioned co-pending application and is concerned with various modifications.